Method for producing hot dip plated steel sheet and apparatus for hot dip plating

Abstract

A method for producing a hot dip plated steel sheet, the method controlling a coating weight by injecting a gas toward a surface of a steel sheet from a time when the steel sheet continuously immersed into a plating bath is pulled up from the plating bath to a time when plating metal adhered onto the surface of the steel sheet is solidified, the method includes: setting an oxygen concentration of a bath surface of the plating bath to be more than or equal to 0.05 vol % and less than or equal to 21 vol % when the gas is injected toward the surface of the steel sheet; and setting an oxygen concentration in a space of an end of the steel sheet at a position where the gas collides with the steel sheet pulled up from the plating bath to be more than or equal to 0.05 vol % and less than or equal to 3 vol % when the gas is injected toward the surface of the steel sheet.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method for producing a hot dip plated steel sheet and an apparatus for hot dip plating used in the method.[0003]Priority is claimed on Japanese Patent Application No. 2008-256208, filed Oct. 1, 2008, the content of which is incorporated herein by reference.[0004]2. Description of Related Art[0005]In a process of producing a hot dip plated steel sheet, a coating weight is controlled by injecting a gas from a wiping nozzle toward a steel sheet during a time when the moving steel sheet (steel strip) is continuously immersed into a plating bath, the steel sheet is pulled up from the plating bath, and then plating metal coated onto a surface of the steel sheet is solidified. At this time, oxide films (dross) are formed on the plated surface of the steel sheet due to the oxidization of the molten plating metal, which degrades the appearance of a product.[0006]In order to prevent the oxidizat...

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Benefits of technology

[0009]The inventors found that the oxide film formation position of the surface of the plated steel sheet is the gas injection position of steel sheet edge (end of the steel sheet) as a result of the repeated studies in order to solve the problems. Thus, the inventors decreased the oxygen concentration in the seal box by installing a seal box smaller than seal boxes of the conventional techniques so as to cover at least the steel sheet edge in the gas injection position where the coating weight is controlled. The inventors found that the formation of the oxide films in the surface of the plated steel sheet can be suppressed and the disadvantages in the operation and quality can be eliminated using this technique, and have contrived the present invention on the basis of this finding.

[0033]In the present invention, in the method for producing the hot dip plated steel sheet and the apparatus for the hot dip plating used in the method, it is possible to decrease the oxygen concentration in the seal box by installing a seal box smaller than seal boxes of the conventional techniques so as to cover at least the steel sheet edge in the gas injection position where the coating weight is controlled. According to the present invention, by means of the technique, it is possible to suppress the formation of the oxide films on the surface of the plated steel sheet and to easily and visually recognize the gas injection position for controlling the coating weight. In addition, it is easy to remove the surface oxide films formed on the surface of the plating bath or to maintain the wiping nozzle. Furthermore, according to the present invention, since it is possible to suppress the generation of zinc fume by the oxide films on the surface of the plating liquid, it is possible to ensure the quality of the plating by preventing metallic zinc from being adhered onto the apparatus such as the wiping nozzle. Thus, according to the present invention, it is possible to use the controlling technique of the coating weight for practical application so as to suppress the formation of the oxide films in the end of the plated steel sheet without degrading the operability and the plating quality.

Problems solved by technology

In addition, it is difficult to remove surface oxide films formed on the surface of the plating bath or to maintain the wiping nozzle.

For this reason, there is a problem in that the operation is inconvenient.

When metallic zinc is adhered to an apparatus such as the wiping nozzle due to the zinc fume, it is not possible to normally perform the wiping operation.

For this reason, there is a problem in that the quality of the product is degraded.

Accordingly, when the techniques are used in a practical application, there is a problem in that the operability and the plating quality are degraded.

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